Magnetic Resonance Image Guided High Intensity Focused Ultrasound (MRgFUS) for Tremor

Language quoted from Centers for Medicare and Medicaid Services (CMS), National Coverage Determinations (NCDs) and coverage provisions in interpretive manuals is italicized throughout the policy. NCDs and coverage provisions in interpretive manuals are not subject to the LCD Review Process (42 CFR 405.860[b] and 42 CFR 426 [Subpart D]). In addition, an administrative law judge may not review an NCD. See Section 1869(f)(1)(A)(i) of the Social Security Act. 

Unless otherwise specified, italicized text represents quotation from one or more of the following CMS sources: 

Title XVIII of the Social Security Act (SSA): 

Section 1862(a)(1)(A) excludes expenses incurred for items or services which are not reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member. 

Section 1862(a)(1)(D) refers to limitations on items or devices that are investigational or experimental. 

Section 1833(e) prohibits Medicare payment for any claim which lacks the necessary information to process the claim.

This LCD addresses use of Magnetic Resonance Guided Focused Ultrasound Surgery System (MRgFUS) for the treatment of neurologic conditions.

MRgFUS unilateral thalamotomy is considered medically reasonable and necessary in patients with all of the following:

1. Medication refractory (ONE)
   1. 1. Essential Tremor (ET) - defined as refractory to at least two trials of medical therapy, including at least one first-line agent
      2. Tremor-Dominant Parkinson's disease (TDPD) (BOTH)
         1. refractory (or intolerant) to levodopa or levodopa equivalent daily dosage (LEDD) ≥ 900 mg
         2. On-medication Unified Parkinson’s Disease Rating Scale (UPDRS) ratio of the mean score for tremor items (items 16, 20, and 21) to the mean postural instability/gait disorder score (items 13-15, 29, and 30) of ≥ 1.5
2. Moderate to severe postural or intention tremor of the hand (defined by a score of ≥2 on the Clinical Rating Scale for Tremor (CRST)
3. Disabling Tremor (defined by a score of ≥2 on any of the eight items in the disability subsection of the CRST)
4. Not a surgical candidate for DBS (e.g., advanced age, anticoagulant therapy, or surgical comorbidities)

MRgFUS Bilateral thalamotomy for Essential Tremor as a staged procedure by at least 9 months from the first thalamotomy is considered medically reasonable and necessary in patients with all of the following:

1. Medication refractory defined as refractory to at least two trials of medical therapy, including at least one first-line agent
2. Moderate to severe postural or intention tremor of the hand (defined by a score of ≥2 on the Clinical Rating Scale for Tremor (CRST)
3. Disabling Tremor (defined by a score of ≥2 on any of the eight items in the disability subsection of the CRST)
4. Not a surgical candidate for DBS (e.g., advanced age, anticoagulant therapy, or surgical comorbidities)

MRgFUS Unilateral pallidotomy is considered medically necessary for the treatment of idiopathic Parkinson’s disease in individuals who meet all of the following criteria:

1. Age 30 or older; and
2. Unilateral pallidotomy is used as an adjunct to medication treatment of idiopathic Parkinson’s disease; and
3. Levodopa responsive (as defined by a 30% or greater reduction in the Movement Disorder Society- Unified Parkinson's Disease Rating Scale [MDS-UPDRS] motor subscale in the on versus off levodopa medication state; and
4. Moderate-to-severe motor complications as defined by at least one of the following:
1. MDS-UPDRS score of 20 or greater in the meds off condition; or
2. Motor complications on optimum medical treatment documented by at least one of the following:
1. Dyskinesia (as defined by MDS-UPDRS item 4.2 score of 2 or greater in the meds on condition); or
2. Motor fluctuations (as defined by MDS-UPDRS item 4.4 score of 2 or greater);
   and
5. The individual is not a candidate for either of the following procedures:
1. Deep brain stimulation (DBS); or
2. Radiofrequency (RF) thermoablation;
   and
6. The absence of all of the following conditions:
1. Central neurodegenerative disease other than Parkinson’s Disease (includes multisystem atrophy, progressive supranuclear palsy, corticobasal syndrome, dementia with Lewy bodies, and Alzheimer’s disease); or
2. Previous deep brain stimulation; or
3. Previous basal ganglia ablation procedure; or
4. Coagulopathy or current anticoagulant use which cannot be reversed; or
5. Intracranial tumor with significant anatomic distortion.

Limitations (not covered):

1. Treatment of head or voice tremor
2. Bilateral thalamotomy for Parkinson's Disease
3. Conditions
   1. other neurodegenerative condition
   2. unstable cardiac disease
   3. untreated coagulopathy
   4. risk factors for deep-vein thrombosis
   5. severe depression (defined by a score ≥20 on Patient Health Questionnaire 9 (PHQ-9) or Beck Depression Inventory score (BDI-II) >14)
   6. cognitive impairment (defined by a score of <24 on the Mini–Mental State Examination, or Montreal Cognitive Assessment (MoCA) score ≤21)
   7. previous brain procedure (transcranial magnetic stimulation, DBS, stereotactic lesioning, or electroconvulsive therapy)
   8. a skull density ratio (of cortical to cancellous bone) <0.40 ± 0.05 as calculated from the screening CT
   9. MRI contraindicated
   10. Drug-induced Parkinsonism
   11. history of seizures, brain tumor, intracranial aneurysm or arteriovenous malformation requiring treatment
   12. pregnancy

Essential tremor (ET)

ET is the most common movement disorder as well as one of the most treated surgically. The prevalence of ET has been estimated at approximately 3% or 10 million people in the United States. While ET does not shorten life expectancy, the associated disabling symptoms, such as hand tremor, can greatly impact quality of life (functional ADLs, work activities, mood, and socialization).

Although there are no curative therapies, symptoms of ET are well managed medically in up to 70% of patients, with surgery reserved for medication-refractory severe impairments. Current surgical options include thalamotomy with radiofrequency (RF) ablation and deep-brain stimulation (DBS); both effectively suppress tremor but require intracranial surgery. Stereotactic radiosurgery (SRS), while non-operative, suffers from delay in tremor reduction (making intraoperative validation impossible), a greater than 10% cumulative risk of adverse events, and theoretical concerns about radiation side effects (6, 22). DBS is currently the intervention of choice, “because of its proven efficacy, reversibility, adjustability, and durability” (22), with thalamotomy “a reasonable alternative….if DBS is not available or practical” (1). This attribute of DBS in creating an adjustable “functional lesion” causes fewer adverse events than thalamotomy (24, 25), and resulted in a general shift away from ablation methods (23).

Neuromodulation with ultrasound energy also required craniotomy until recently; advances in ultrasound transducer design and high-resolution magnetic resonance imaging now allow precise transcranial delivery of high-intensity focused ultrasound. The ultrasound causes a local increase in temperature in the target tissue, resulting in coagulation necrosis while sparing the surrounding normal structures. In addition to providing location guidance, MRI provides real-time clinical monitoring of treatment intensity via thermal imagery. On 1/1/16, a CPT Category III tracking code specific to MRgFUS treatment of movement disorder became effective. FDA PMA approval for the Magnetic Resonance Guided Focused Ultrasound Surgery System (MRgFUS) (Exablate Model 4000, InSightec, Inc.) “for the unilateral thalamotomy treatment of idiopathic essential tremor patients with medication-refractory tremor” came on 7/11/16 (3).

Among the peer-reviewed clinical studies of MRgFUS for the treatment of medication-refractory ET, all but one were small, uncontrolled, pilot studies with short follow-up (4-11). FDA approval for MRgFUS treatment of ET was based on its pivotal study, a prospective, double-blind, randomized, sham-controlled trial (RCT) of MRgFUS to create a unilateral thalamic ablation for the treatment of ET (12). Seventy-six patients with moderate-to-severe essential tremor refractory to at least two trials of medical therapy were randomized in a 3:1 ratio to either MRgFUS or a sham procedure. The primary endpoint, the CRST at 3 months, was significantly improved in the MRgFUS group (p<0.001). Secondary outcome measures, including disability and quality of life, were also significantly improved. However, both hand and total tremor scores steadily deteriorated over the year, 23% and 38% respectively. In fact, this drop in efficacy and the limited follow-up period were cited as major concerns in the accompanying editorial which advocates for much longer follow-up (2-5 years or more) to demonstrate sustained benefit (2). Another concern was persistent adverse neurologic effects in the MRgFUS group at 12 months, including gait disturbance (9%) or numbness (14%).

Two-year follow-up on sixty-seven of the patients demonstrated durable improvement in tremor at 1 year (53%; 8.9 ± 4.8; 70 patients) and at 2 years (56%; 8.8 ± 5.0; 67 patients). Disability score improved throughout this period, none of the adverse effects worsened, two resolved, and there were no new delayed complications (27).

The editorial concludes that “A head-to-head comparison with DBS would facilitate the direct comparison of the two approaches.” Some contend that a direct comparative trial between MRgFUS and DBS will be unlikely “due to the significant differences in invasiveness of the two procedures.” Interestingly, a letter to the editor agrees a direct comparative study isn’t warranted, but apparently for the opposite ethical reason, noting “that the high rate of adverse events that is consistently reported with thalamotomy of any kind suggests that equipoise does not exist” (13). While it is true that MRgFUS is less invasive than DBS in terms of not requiring cranial penetration with hardware, it is more invasive than DBS in the creation of a fixed thalamic brain lesion, which can result in permanent neurologic deficit.

A recently published meta-analysis is meant to provide “an approximation of an RCT” head-to-head comparison between MRgFUS, DBS, and SRS; the authors claim an actual RCT is unlikely (22). Pre- and postoperative tremor-related disability scores were collected from 32 studies involving 83 MRgFUS, 615 DBS, and 260 SRS cases. MRgFUS thalamotomy resulted in significantly higher utility scores (defined as quality of life and derived from percent change in functional disability) compared with DBS (P < 0.001) or SRS (P < 0.001). The authors conclude that “preliminary experience with MRgFUS supports its broad adoption for medically refractory ET.”

A retrospective analysis of 59 patients who underwent unilateral treatment for drug-resistant ET with RF thalamotomy (n=17), DBS (n=19), and MRgFUS (n=23) showed no statistical differences in tremor severity improvement at 1 month or 1 year follow-up (23). However, MRgFUS had a significantly lower complication rate (p < 0.01) at 1 year (4.4%) compared with RF (11.8%) and DBS (21.1%). The authors conclude that “MRgFUS is a promising therapy with the potential to replace DBS for patients who cannot tolerate DBS, the standard surgical treatment for ET,” but that “the long-term effects of MRgFUS should be systematically evaluated in a future prospective, randomized study in order to demonstrate whether MRgFUS provides superior management of ET symptoms.”

Tremor-Dominant Parkinson’s disease (TDPD)

Tremor is a common motor feature of Parkinson disease (PD), and TDPD is a clinical subtype distinct from the akinesia/rigidity (AR) and postural instability/gait disorder subtypes. This subtype may be more resistant to dopamine-replacement therapy than other motor symptoms. DBS and traditional thalamic lesioning are accepted treatments of motor symptoms of PD. Several small observational studies also demonstrated efficacy of MRgFUS thalamotomy in TDPD out to one year (30-32).

A small prospective, sham-controlled RCT looked at the safety and efficacy of unilateral MRgFUS thalamotomy at 3 and 12 months in patients with TDPD (28). Twenty-seven patients (median age 67.8 years; interquartile range [IQR], 62.1-73.8) were randomized (2:1) to MRgFUS (20) vs. sham (7). Predefined primary outcomes were safety and difference in improvement between groups at 3 months in the on-medication treated hand tremor CRST subscore. Secondary outcomes included descriptive results of UPDRS scores and quality of life measures. Three-month on-medication median tremor scores improved 62% (17 to 4.5; IQR, 22%-79%) in the treatment group, and 22% (23 to 17; IQR, −11% to 29%) in the sham group (P = .04). Secondary outcomes showed non-statistical improvement trends in the treatment group. At 3 months, 6 sham patients crossed-over to MRgFUS treatment. Three months after crossover the median baseline CRST score improved from 21 to 5.5, similar to the 3 months outcomes in the group originally allocated to treatment. One-year follow-up of 14 treatment and 5 sham crossover patients demonstrated CRST score maintenance. Early in the study, heating of the internal capsule resulted in 2 cases (8%) of mild hemiparesis, which improved and prompted monitoring of an additional axis during magnetic resonance thermometry. Other persistent adverse events were orofacial paresthesia (20%), finger paresthesia (5%), and ataxia (5%).

On 12/16/2018, the Exablate MRgFUS device FDA indication was expanded to include unilateral thalamotomy (ventralis intermedius) treatment of TDPD with medication-refractory tremor in patients at least age 30 (29). UpToDate recommends consideration of MRgFUS thalamotomy in selected TDPD patients who are not candidates for DBS (33).

A reconsideration request dated March 17, 2023 asked for several changes in the policy.

1. To allow MRgFUS in the unilateral pallidotomy of patients with advanced, idiopathic Parkinson’s disease with medication-refractory moderate to severe motor complications as an adjunct to Parkinson’s disease medication treatment.
2. Removal of the use of dominant hand from the Coverage Guidance under MRgFUS unilateral thalamotomy in those with essential tremor.
3. Removal of bilateral thalamotomy as a limitation.

The use of MRgFUS in the unilateral pallidotomy of patients with advanced, idiopathic Parkinson’s disease with medication-refractory moderate to severe motor complications as an adjunct to Parkinson’s disease medication treatment is not yet ready for widespread use after review of the article in the New England Journal of Medicine (Feb 23, 2023) “Trial of Globus Pallidus Focused Ultrasound Ablation in Parkinson’s Disease”. Patients with Parkinson’s disease and dyskinesia or motor fluctuations and motor impairment in the off-medication state were randomly assigned in a 3:1 ratio to either focused ultrasound ablation opposite the most symptomatic side of the body or a sham procedure. The primary outcome was a response at 3 months, defined as a decrease of at least 3 points from baseline either in the score on the Movement Disorders Society–Unified Parkinson’s Disease Rating Scale, part III (MDS-UPDRS III), for the treated side in the off-medication state or in the score on the Unified Dyskinesia Rating Scale (UDysRS) in the on-medication state. Secondary outcomes included changes from baseline to month 3 in the scores on various parts of the MDS-UPDRS. After the 3-month blinded phase, an open-label phase lasted until 12 months. The results showed of 94 patients, 69 were assigned to undergo ultrasound ablation (active treatment) and 25 to undergo the sham procedure (control); 65 patients and 22 patients, respectively, completed the primary-outcome assessment. In the active-treatment group, 45 patients (69%) had a response, as compared with 7 (32%) in the control group (difference, 37 percentage points; 95% confidence interval, 15 to 60; P = 0.003). Of the patients in the active-treatment group who had a response, 19 met the MDS-UPDRS III criterion only, 8 met the UDysRS criterion only, and 18 met both criteria. Results for secondary outcomes were generally in the same direction as those for the primary outcome. Of the 39 patients in the active-treatment group who had a response at 3 months and who were assessed at 12 months, 30 continued to have a response. Pallidotomy-related adverse events in the active-treatment group included dysarthria, gait disturbance, loss of taste, visual disturbance, and facial weakness. The conclusions stated that longer and larger trials are required to determine the effect and safety of this technique.

The accompanying editorial from the NEJM summarizes this study. “The results confirm that it is effective in reducing motor complications of Parkinson’s disease, at least in the short term. However, the degree of improvement was less than suggested by previous open-label studies.” “Nevertheless, the results suggest that not all patients derived a meaningful benefit from the intervention. The supplementary data provide preliminary information indicating that patients who were younger, had lower motor severity scores, or had higher dyskinesia scores were more likely to benefit, but the population most likely to benefit needs to be examined in further studies. As with other surgical interventions in Parkinson’s disease, evaluation of benefit requires longer-term follow-up to establish the overall effect on patients’ functioning. The results of this trial are promising, but given the nonreversible nature of the intervention and the progressive nature of the disease, it will be important to establish whether improvements in motor complications are maintained over longer periods and whether treatment results in improved overall functioning and quality of life for patients.”

Safety and efficacy of unilateral focused ultrasound pallidotomy on motor complications in Parkinson's disease: a systemic review and meta-analysis from Neurological Sciences June 24, 2024, was reviewed. A meta-analysis was done to evaluate the safety and efficacy of unilateral focused ultrasound pallidotomy on motor complications in Parkinson's disease patients. They identified studies relevant to unilateral focused ultrasound pallidotomy and Parkinson's disease. It included observational studies, clinical trials and case series reporting the impact of the intervention on motor complications in Parkinson's disease patients. Five studies were included in the meta-analysis involving 112 Parkinson's disease patients undergoing the procedure. There was a significant improvement from baseline. It appears that the effect of the procedure on motor complications is effective with a significant decrease in the UPDRS and the UDYSRS, reflecting improvement. The incidence of adverse effects was not statistically significant.

Parkinson's disease is a neurodegenerative disorder that affects the central nervous system and is characterized by progressive loss of dopaminergic neurons in the substantia nigra of the brain. Primary features include tremors, rigidity, bradykinesia and postural instability in addition to a host of other associated symptoms. There are two main treatments through surgery which are ablation and modulation. Ablation entails performing thalamotomy for PD primarily characterized by tremor predominant Parkinson's disease and pallidotomy for conventional Parkinson disease. Modulation is currently achieved using deep brain stimulation which is an intervention that involves implanting electrodes in the brain to stimulate specific areas which can help alleviate motor symptoms. Thalamotomy and pallidotomy are traditionally carried out through radiofrequency lesioning which involves invasive access through a small hole of the cranium and penetration within RF probe. Procedures that involve intrusions such as thalamotomy and DBS carry the potential for complications like infection, bleeding and malfunction of the hardware. 

In order to create lesions in the brain, high frequency focused ultrasound offers a noninvasive approach. There is an FDA approved system in the United States for essential tremor and Parkinson's disease. At the time of the article being written, focused ultrasound was only approved for unilateral pallidotomy of medication refractory Parkinson's patients with moderate to severe tremors or dyskinesia. There are studies being organized to assess the use of this bilaterally.

Focused ultrasound is becoming more popular because it can treat patients who are not suitable for surgery, and it is relatively safe compared to other invasive options, but it is disadvantaged by its irreversible nature. Further research is needed to look at sub-thalamotomy for Parkinson's disease and other forms of parkinsonism. Focused ultrasound provides a 1-time solution without the need for follow up procedures or visits for battery replacement, wire repair or simulator adjustments, which is potentially seen with DBS. MRgFUS also does not harm healthy tissue or carry the risk of infections from implanting a foreign object.

Bilateral thalamotomy for essential tremor will now be allowed and removal of the use of the word dominant will occur with this reconsideration. This will be based on the information in the FDA letter dated December 8, 2022 referenced as P150038/S022 to the manufacturer of Exablate Model 4000 Type 1.0 and 1.1 System (“Exablate Neuro").

In summary, MRgFUS is a promising new treatment approach that has attributes, positive and negative, distinct from both traditional thalamotomy and DBS. However, long-term effectiveness and safety remain uncertain (1, 23) and warrant a direct comparison with DBS, the current surgical standard.

However, given the support for traditional thalamotomy, generally, as an alternative “if DBS is not available or practical”, and the support for MRgFUS thalamotomy, specifically, as an alternative in patients “who are not a candidate for DBS” by the American Association of Neurological Surgeons (AANS), Congress of Neurological Surgeons (CNS) and the American Association of Stereotactic and Functional Neurosurgery (ASSFN), NGS considers MRgFUS reasonable and necessary in that context. 

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1. Tarsy D, Shih L. Surgical treatment of essential t tremor. http://www.uptodate.com/contents/surgical-treatment-of-essential-tremor.

2. Louis LD. Treatment of medically refractory essential tremor. N Engl J Med. 375;8:792-793.

3. FDA approval ExAblate Neuro. https://www.accessdata.fda.gov/cdrh_docs/pdf15/P150038a.pdf. Accessed 7/23/17.

4. Jeanmonod D, Werner B, Morel A, et al. Transcranial magnetic resonance imaging–guided focused ultrasound: noninvasive central lateral thalamotomy for chronic neuropathic pain. Neurosurg Focus. 2012;32(1):1-11.

5. Lipsman N, Schwartz ML, Huang Y, et al. MR-guided focused ultrasound thalamotomy for essential tremor: a proof-of-concept study. Lancet Neurol. 2013;12(5):462-468.

6. Elias WJ, Huss D, Voss T, et al. A pilot study of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 2013;369:640-648.

7. Wintermark M, Druzgal J, Huss DS, et al. Imaging findings in MR imaging-guided focused ultrasound treatment for patients with essential tremor. Am J Neuroradiol. 2014;35(5):891-896.

8. Chang WS, Jung HH, Kweon EJ, Zadicario E, Rachmilevitch I, Chang JW. Unilateral magnetic resonance guided focused ultrasound thalamotomy for essential tremor: practices and clinicoradiological outcomes. J Neurol Neurosurg Psychiatry. 2015;86(3):257-264.

9. Huss DS, Dallapiazza RF, Shah BB, Harrison MB, Diamond J, Elias WJ. Functional assessment and quality of life in essential tremor with bilateral or unilateral DBS and focused ultrasound thalamotomy. Mov Disord. 2015;30(14):1937-1943.

10. Jung HH, Chang WS, Rachmilevitch I, Tlusty T, Zadicario E, Chang JW. Different magnetic resonance imaging patterns after transcranial magnetic resonance–guided focused ultrasound of the ventral intermediate nucleus of the thalamus and anterior limb of the internal capsule in patients with essential tremor or obsessive-compulsive disorder. J Neurosurg. 2015;122:162-168.

11. Gallay MN, Moser D, Rossi F, et al. Incisionless transcranial MR-guided focused ultrasound in essential tremor: cerebellothalamic tractotomy. J Ther Ultrasound. 2016;4:5. DOI 10.1186/s40349-016-0049-8.

12. Elias WJ, Lipsman N, Ondo WG, et al. A randomized trial of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 2016;375:730-739.

13. Alterman RL. A trial of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 375;22:2201-2203.

14. Novitas LCD Services That Are Not Reasonable and Necessary (L35094).

15. Noridian LCD Non Covered Services (L36219).

16. First Coast Service Options LCD Noncovered Services (DL33777).

17. Palmetto GBA LCD Non-Covered Category III CPT Codes (DL34555).

18. BCBSMA Policy Number 243. Magnetic Resonance-Guided Focused Ultrasound. BCBSMA Policy. Accessed 7/23/17.

19. Aetna Policy Number 0153. Thalamotomy. http://www.aetna.com/cpb/medical/data/100_199/0153.html. Accessed 7/23/17.

20. UnitedHealthcare Guideline Number MPG043.05. Category III CPT Codes. United Healthcare Guideline.

21. Anthem Policy Number MED.00057. MRI Guided High Intensity Focused Ultrasound Ablation for Non-Oncologic Indications. Anthem Policy. Accessed 7/23/17.

22. Ravikumar VK, Parker JJ, Hornbeck TS, et al. Cost-effectiveness of focused ultrasound, radiosurgery, and DBS for essential tremor. Mov Disord. 2017;32(8):1165-1173.

23. Kim M, Jung NY, Park CK, Chang WS, Jung HH, Chang JW. Comparative Evaluation of Magnetic Resonance-Guided Focused Ultrasound Surgery for Essential Tremor. Stereotact Funct Neurosurg. 2017;95(4):279-286.

24. Zesiewicz TA, Elble R, Louis ED, et al. Practice parameter: therapies for essential tremor: report of the Quality Standards Subcommittee of the American Academy of Neurology. Neurology. 2005;64(12):2008-2020.

25. Zesiewicz TA, Elble RJ, Louis ED, et al. Evidence-based guideline update: treatment of essential tremor: report of the Quality Standards subcommittee of the American Academy of Neurology. Neurology. 2011;77(19):1752-1755.

26. Schuurman PR, Bosch DA, Bossuyt PM, et al. A comparison of continuous thalamic stimulation and thalamotomy for suppression of severe tremor. N Engl J Med. 2000;342(7):461-468.

27. Chang JW, Park CK, Lipsman N, et al. A prospective trial of magnetic resonance-guided focused ultrasound thalamotomy for essential tremor: Results at the 2-year follow-up. Ann Neurol. 2018;83(1):107-114.
    
    
28. Bond AE, Shah BB, Huss DS, et al. Safety and efficacy of focused ultrasound thalamotomy for patients with medication-refractory, tremor-dominant Parkinson disease: a randomized clinical trial. JAMA Neurology. 2017;74(12):1412-1418.
    
    
29. Food and Drug Administration. Exablate Model 4000 Types 1.0 and 1.1 System Summary of Safety and Effectiveness Data. December 16, 2018. https://www.accessdata.fda.gov/cdrh_docs/pdf15/P150038S006B.pdf Accessed 6/3/20.
    
    
30. Schlesinger I, Eran A, Sinai A, et al. MRI Guided Focused Ultrasound Thalamotomy for Moderate-to-Severe Tremor in Parkinson's Disease. Parkinsons Dis. 2015;2015:219149.
    
    
31. Fasano A, Llinas M, Munhoz RP, Hlasny E, Kucharczyk W, Lozano AM. MRI-guided focused ultrasound thalamotomy in non-ET tremor syndromes. 2017;89(8):771-775.
    
    
32. Zaaroor M, Sinai A, Goldsher D, Eran A, Nassar M, Schlesinger I. Magnetic resonance-guided focused ultrasound thalamotomy for tremor: a report of 30 Parkinson's disease and essential tremor cases. J Neurosurg. 2018;128(1):202-210.
    
    
33. UpToDate: Device-assisted and lesioning procedures for Parkinson disease. https://www.uptodate.com/contents/device-assisted-and-lesioning-procedures-for-parkinson-disease?search=deep%20brain%20stimulation%20parkinsons&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H3670506581. Accessed 6/4/20.

34. Krishna V, Fishman PS, Eisenberg HM, et al. Trial of Globus Pallidus Focused Ultrasound Ablation in Parkinson's Disease. N Engl J Med. Feb 23 2023;388(8):683-693. doi:10.1056/NEJMoa2202721

35. Schrag A. Focused Ultrasound Ablation of the Globus Pallidus Internus for Parkinson's Disease. N Engl J Med. Feb 23 2023;388(8):759-760. doi:10.1056/NEJMe2215506

36. Food and Drug Administration. Exablate Model 4000 Type 1.0 and 1.1 System (“Exablate Neuro”) Premarket Approval (PMA) (fda.gov) Accessed 6/17/2024.

37. Food and Drug Administration. Exablate Model 4000 Types 1.0 and 1.1 System Summary of Safety and Effectiveness Data. October 29, 2021. P150038S014B.pdf (fda.gov) Accessed 6/17/2024.

38. Abbas, A., et al., Safety and efficacy of unilateral focused ultrasound pallidotomy on motor complications in Parkinson's disease (PD): a systematic review and meta-analysis. Neurol Sci, 2024. 45(10): 4687-4698.

39. Krishna, V., et al., Trial of Globus Pallidus Focused Ultrasound Ablation in Parkinson's Disease. N Engl J Med, 2023. 388(8): 683-693.

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